Mycoplasma gallisepticum infectious disease, that is one of the most serious infections on poultry such as chickens, etc., is characterized by chronic respiratory impairment accompanied by inflammation of the air sac in chicken. When chickens were infected with Mycoplasma gallisepticum, an egg-laying rate and a hatching rate of eggs produced by infected chickens are markedly reduced. As the result, shipping of eggs and egg-laying chickens decrease so that a considerable economic loss is caused. In addition, Mycoplasma gallisepticum infection induces the reduction in immunity so that chickens are liable to suffer from other infectious diseases to cause complication of severe infectious diseases. Furthermore, Mycoplasma gallisepticum is known to be a pathogen of sinusitis in turkeys.
The present inventors already found proteins react with antisera against Mycoplasma gallisepticum (Japanese Patent Application Laid-Open No. 2-111795). It is expected that these proteins would be useful as vaccines for preventing Mycoplasma gallisepticum infections, but in order to prepare more potent vaccines, it is desired to provide proteins having a higher activity.